This invention relates generally to a control circuit for small electrical appliances which have an inductive load. In particular, this invention concerns a touch control circuit for a fan motor, used either in a stand-alone fan or in an appliance incorporating a fan.
Fans are well known in the art and are commonly used both independently to circulate air and in conjunction with other small appliances such as heaters, humidifiers, and air purifiers to effectuate the underlying function of the appliance. Conventional fans and small appliances which use fans typically utilize switches that require manual manipulation for adjusting the power intensity of the fan unit. In other industries and for other household products with typically resistive loads, such as lighting fixtures, there has arisen a body of technology for providing a variety of touch control switches. These range in sensitivity from a light touch (or even close proximity) to being sensitive only to firm pressure. Technically there are various capacitive, resistive, and inductive types of switches as well as other forms providing a greater degree of remoteness in control (as using infra-red or ultrasonics, or audio (the clapper) which are known in the field of switch technology. Some of these approaches have been used to control the power state within lamps and large appliances. Some of these approaches, as applied to touchscreen computer displays, are compared in an article entitled "Touchscreens are changing the face of computers" in Electronic Products November, 1994 pp. 63-70 incorporated herein by reference.
U.S. Pat. No. 5,166,482 to Li, dated Nov. 24 1992, discloses an external, remote touch control lamp switch that includes an outer shell, a touch-control metal panel over the outer shell, a control circuit board fastened inside the outer shell to receive a touch-control signal from the panel, and a socket fastened in the outer shell to connect to the male prongs in a lamp plug and to transmit an ON/OFF signal to the lamp responsive to a touch. Such a switch is remote to the lamp, however, and was motivated by the inconveniences and structural problems associated with common internal touch control lamp switches.
U.S. Pat. No. 4,668,876 to Skarman, dated May 26, 1987, correspondingly discloses a remote touch control switch and lamp system that includes a remote touch control circuit with an electrical lead connected to a conductive portion of a lamp or lamp housing. A special type of lamp cord is required, however, for proper operation of the switch and lamp system. Although lamps are the primary disclosed devices that are used in combination with the remote switch, Skarman also briefly suggests that the remote switch may be adapted to be used in conjunction with a fan. There is no suggestion or hint, however, of a fan having an integrally mounted touch control switch. Moreover, Skarman specifically teaches away from an internal switch used in combination with a lamp or any other electrical appliance. Such a combination as mentioned in Skarman would require additional modification of the lamp or appliance, something Skarman wishes to avoid.
For light (soft) touch control, there are a number of options presented in the literature for controlling lamps. A typical control circuit consists of several elements as disclosed in U.S. Pat. No. 4,831,279 to Ingraham and U.S. Pat. No. 3,666,988 to Bellis, both incorporated herein by reference, of an oscillator which is set so that the frequency of oscillation is changed for a change in input capacitance or voltage. Some such circuits generally also incorporate a triac for electronically switching moderate power levels. See, for instance, U.S. Pat. No. 4,701,676 to Gibson, and Galloway "Using the Triac for Control of AC Power", General Electric Application Note No. 200.35, March 1966, p. 16. However, switching modes disclosed (as in Gibson) require complex electronics and timing circuits.
In one instance, primarily for a light control application (U.S. Pat. No. 4,701,676 to Gibson), a means for balancing impedances on the input side of the touch control circuitry is disclosed. This disclosure does not extend to suggesting a need to balance impedances on the output side of the control circuitry.
With respect to the point of contact, there are several options. One option is to have the whole appliance or lamp itself be conducting and serve as the point of contact. This approach presents a risk of electrical shock. A second option is to have a special metallic conducting plate located on the appliance. A third option is to have a non-metallic material connected to the input of a capacitively linked sensor circuit. Examples of this are given in the following.
U.S. Pat. No. 4,665,040 to Ogino et. al., dated May 12, 1987, discloses a specific touch control switch for electrical appliances. Ogino teaches the internal structure of a type of switch as it discloses the use of the switch as merely for use in conjunction with electric appliances. There is no suggestion to utilize the disclosed switch, nor any similar switch, internally in combination with a motor or appliance which uses an inductive load such as a fan.
U.S. Pat. No. 4,380,040 to Posset, dated Apr. 12, 1983, also discloses a specific type of switch for use in touch control systems. In like manner to Ogino, Posset discloses the internal structure of a type of switch as it teaches its use in touch control systems. Again, there is no suggestion to utilize the switch internally singularly or in combination with small appliances such as fan motors which may have varying degrees of inductances, capacitances and other phase-shifting configurations.
U.S. Pat. No. 4,119,864 to Petrizio, incorporated herein by reference, suggests two means to signal the system of one's intentions regarding different power levels. The two means are by the length of time a touch switch is actuated, and by the number of times it is actuated. Neither of these approaches are specifically applied to appliances of the type identified in the present invention.
In summary, there are a number of switching systems described in the literature. The approaches may be distinguished as:
(1) switches remote to the appliance versus switches integral to the appliance;
(2) switches for single power mode (ON or OFF) versus switches to provide multiple levels;
(3) systems without signal conditioning versus systems with signal conditioning; and
(4) electro-mechanical switches versus electronic or solid state switches.
Electronic or solid state switches usually consist of a signal detection stage and a signal conditioning stage. Signal conditioning to reduce false triggering from spurious voltage fluctuations may be as simple as an R-C filter or as complex as using comparators or timing sequences. The signal detection stage for electronic switches falls into one of three broad classes:
Class 1, those activated by pressure (as changing the capacitance by decreasing the distance between conducting plates or changing the resistance of a capsule of conducting elements);
Class 2, those activated by the introduction of an outside capacitance or voltage source (as from a person acting as an antenna for electromagnetic signals); and
Class 3, those activated by a change in inductance brought about by the introduction of objects into an electromagnetic field.
In the latter instance, no physical contact is required to have "touch" control. In Class 1, by contrast, substantial pressure is frequently required. In Class 2, a very light touch or a very close nearness is sufficient. For reasons of economy, functionality, and simplicity, we determined to create an invention of the Class 2 type. We discovered that referenced circuits used for the control of lighting often failed when trying to control motors as used in fans, because depending upon the motor type, there were capacitive or inductive loads which introduced phase shifts which interfered with operation of the solid state switches commercially available.
Accordingly, there is a need for a device that overcomes these problems, namely, a device which provides the combination of an internal fully integrated touch control system switch including signal conditioning, impedance matching, and power level adjustment which functions independently or in conjunction with other appliances.
Furthermore, the touch control switch offers advantages over the typical mechanical switch, since a mechanical switch is not convenient to operate, especially for disabled and otherwise handicapped people. Actually twisting or pushing a manual switch to operate a fan or other appliance is more than a mere inconvenience for the disabled and is often an impossibility. More broadly, heaters, cooling fans and other air treatment appliances are generally placed on the floor requiring one to bend over and to manipulate controls while in an awkward position. For these and other reasons, there is a need to provide alternatives to conventional electro-mechanical switches for control of household appliances.